--- a/dom/animation/KeyframeEffectReadOnly.cpp
+++ b/dom/animation/KeyframeEffectReadOnly.cpp
@@ -281,19 +281,22 @@ KeyframeEffectReadOnly::UpdateProperties
   MOZ_DIAGNOSTIC_ASSERT(!mIsComposingStyle,
                         "Should not be called while processing ComposeStyle()");
   if (mIsComposingStyle) {
     return;
   }
 
   nsTArray<AnimationProperty> properties = BuildProperties(aStyleContext);
 
+  // FIXME (bug 1329878): Do this for servo too.
   // We need to update base styles even if any properties are not changed at all
   // since base styles might have been changed due to parent style changes, etc.
-  EnsureBaseStyles(aStyleContext, properties);
+  if (aStyleContext->PresContext()->StyleSet()->IsGecko()) {
+    EnsureBaseStyles(aStyleContext, properties);
+  }
 
   if (mProperties == properties) {
     return;
   }
 
   // Preserve the state of the mIsRunningOnCompositor flag.
   nsCSSPropertyIDSet runningOnCompositorProperties;